Expandable stent delivery system with outer sheath

ABSTRACT

According to aspects described herein, there is disclosed an improved hot balloon catheter delivery system for shape memory tubular stents is disclosed. An outer sheath is provided on the delivery system that facilitates stent placement on a balloon during delivery through an endoscope. In one embodiment, the stent may be positioned between radiopaque markers/electrodes and the balloon may be heated. The stent may be prevented from moving proximally relative to the catheter as the delivery system is tracked through the patient&#39;s anatomical passageways. The outer sheath may be positioned to ride over the proximal cone of the hot balloon catheter and abut the proximal end of the stent to facilitate proper alignment of the balloon for deployment. Upon deployment of the stent in an appropriate position, the sheath may be pulled away from the stent to expose the proximal cone of the balloon and thereby allow balloon and stent expansion.

PRIORITY CLAIM

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/021,064 filed on Jan. 15, 2008.

TECHNICAL FIELD

The present disclosed technologies generally relate to stent deliverysystems and more particularly to an outer sheath addition to hot ballooncatheter delivery systems for shape memory tubular stents.

BACKGROUND

A stent is generally a longitudinal tubular device formed ofbiocompatible material, which is useful to open and support variouslumens in the body. Stents are used in various bodily passageways, suchas in the coronary or peripheral vasculature, esophagus, trachea,bronchi, colon, biliary tract, urinary tract, prostate, brain, as wellas in a variety of other applications in the body. These devices areimplanted within the passage to open and/or reinforce collapsing orpartially occluded sections. While stents and other intraluminaryprosthesis are foreign objects to the human body, they are designed toremain within a body passageway for prolonged periods or evenindefinitely.

Stents generally include a flexible configuration. This configurationallows the stent to be inserted through curved vessels or lumens(natural or artificial) and curved instruments, such as an endoscope.Such stents are generally delivered using a flexible elongate catheter.The catheters are designed to resist kinking and may be developed withvarious levels of stiffness. The stents are designed and configured toradially compress for intraluminary catheter implantation. Once properlypositioned adjacent the damaged vessel or lumen, the stent is radiallyexpanded so as to support and reinforce the vessel or lumen. Radialexpansion of the stent may be accomplished by inflation of a balloon orother expanding means attached to the catheter or the stent may be ofthe self-expanding variety which will radially expand once deployed.

Tubular shaped structures, which have been used as intraluminaryvascular stents, have included helically wound coils which may haveundulations or zigzags therein, slotted stents, ring stents, braidedstents and open mesh wire/filament stents, to name a few. Additionally,super-elastic and shape memory materials using plastic and/or metalshave also been used to form stents.

Diagnosis and treatment in patients of biliary strictures caused bymalignant or benign biliary disease is treatable. A patient with biliarydisease typically suffers from an obstruction in the pancreaticobiliaryductal system. Numerous diseases can cause the inability of bile flow,however, the presence of gallstones and/or strictures appear the mostprevalent reason. For benign strictures, stenting is one possiblesolution. In particular, tubular stents are used in bile, pancreatic andhepatic ducts where a solid stent is needed and where in-growth canoccur due to proliferating oncologous cells.

Solid stents are often mounted on a balloon catheter and deliverednon-invasively, such as through an endoscope, and deployed by expandingthe stent to a larger diameter. For example, U.S. Pat. No. 5,191,883 toLennox et al. and U.S. Pat. No. 6,830,559 to Schock describe ballooncatheter delivery systems. Alternatively, the stent is slipped off acatheter with no expansion. For example, see U.S. Pat. No. 5,334,185 toGiesy et al. These stents are typically designed to withstand drasticdeformations as it is conveyed through the twists and turns of thetortuous anatomy of a patient's gastrointestinal system.

One drawback, however, is that as the delivery system is tracked throughthe endoscope, the stent may slide out of its intended position. Inparticular, a stent may slide proximally and may no longer be disposedbetween radiopaque markers on and/or the electrodes used to expand theballoon located on the delivery system. Thus, once out of position, thephysician may find it difficult to accurately position the stent. Also,the stent may be difficult to properly expand if improperly positionedon the balloon.

Additionally, even when the stent remains properly positioned on thedelivery system, removal of the balloon after delivery can sometimes beproblematic. After the stent has been fully expanded, the balloon isgenerally deflated before being removed. While or after being deflated,however, the balloon may get stuck to the stent. Sticking can occur dueto anatomical curvatures in the delivery location which pinch or trapthe balloon, stent to balloon material tackiness, a balloon wing foldgetting hung-up and/or other reasons. During removal, if the balloon isstuck to the stent it can slightly pull the stent out of place or evencompletely out of position.

Therefore, there is a need for improved delivery systems for stentsdeployed using an expansion member, such as a balloon catheter. Such asystem preferably overcomes the shortcomings set forth above while beingrelatively easily manufactured and use.

SUMMARY

An improved hot balloon catheter delivery system for shape memorytubular stents is disclosed. An outer sheath is provided on the deliverysystem that facilitates stent placement on a balloon during deliverythrough an endoscope. In one embodiment, the stent may be positionedbetween radiopaque markers/electrodes and the balloon may be heated. Thestent may be prevented from moving proximally relative to the catheteras the delivery system is tracked through the patient's anatomicalpassageways. The outer sheath may be positioned to ride over theproximal cone of the hot balloon catheter and abut the proximal end ofthe stent to facilitate proper alignment of the balloon for deployment.Upon deployment of the stent in an appropriate position, the sheath maybe pulled away from the stent to expose the proximal cone of the balloonand thereby allow balloon and stent expansion.

One aspect of the disclosed technology includes an apparatus fordelivering an expandable stent into a patient through a body lumen. Theapparatus includes a flexible catheter, an expansion member, a controlassembly and a sheath member. The flexible catheter is for deliveringthe stent. The catheter may have a stent delivery portion at a distalend thereof. The expansion member may be secured to the stent deliveryportion of the catheter. The expansion member may be adjustable betweena collapsed state and an expanded state. The expandable stent is mountedon and circumferentially surrounds at least a portion of the expansionmember, whereby adjustment of the expansion member from the collapsedstate to the expanded state causes radial expansion of the stentrelative to a longitudinal axis of the stent. The control assembly mayactuate the expansion member between the collapsed and the expandedstates. The sheath circumferentially surrounds a portion of the catheterfor limiting movement of the stent in relative to the catheter duringdelivery.

Another aspect of the disclosed technology includes an assembly fordelivering a stent into a patient through a body lumen. The assemblyincludes an expandable stent, a flexible catheter, an expansion member,a control assembly and a sheath. The flexible catheter is for deliveringthe stent. The expansion member may be secured to a distal end of thecatheter. The expansion member may be adjustable between a collapsedstate and an expanded state. Also, the stent may be mounted on at leasta portion of the expansion member, whereby adjustment of the expansionmember from the collapsed state to the expanded state causes radialexpansion of the stent relative to a longitudinal axis of the stent. Thecontrol assembly may actuate the expansion member between the collapsedand the expanded states. Also, the sheath circumferentially surrounds aportion of the catheter for limiting movement of the stent relative tothe catheter.

Additionally, the expansion member may comprise a balloon. The ballooncan include two opposed ends that when inflated during delivery arewider than a central portion of the balloon. Further, the sheath can bemoveable along a length of the catheter. The sheath can be securablerelative to the catheter for limiting the stent movement. Also, a distalend of the sheath can abut a proximal end of the stent. Further a distalend of the sheath can be radially wider than a central portion of thesheath. A distal end of the sheath can flare radially outwardly and/orinclude one or more slits passing through a wall of the sheath.

Yet another aspect of the disclosed technology includes a method fordelivering an expandable stent into a patient through a body lumen. Themethod comprises providing a flexible balloon catheter for deliveringthe stent. The catheter includes an expandable balloon, a controlassembly and an outer sheath. The balloon may be secured to a distal endof the catheter and may be adjustable between a collapsed state and anexpanded state. The control assembly may adjust the expansion memberbetween states. Additionally, the method comprises mounting a stent onthe balloon in the collapsed state. A distal end of the sheath may abuta proximal end of the stent for limiting movement of the stent relativeto the catheter. Additionally, the method comprises inserting theflexible catheter and stent into a patient through a body lumen, whilemaintaining a fixed relative position between the stent and thecatheter. Then, the control assembly is activated to expand the stent.Thereafter, the balloon catheter may be withdrawn once the stent hasexpanded. The method can further include the step of advancing thesheath distally inside the stent prior to withdrawing the catheter.

These and other embodiments, features, and advantages of the disclosedtechnologies will become apparent from the following detaileddescription of illustrative embodiments thereof, which is to be read inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one aspect of a stent delivery systemaccording to the disclosed technology.

FIGS. 2A-D are sectional views of one embodiment the distal end of thestent delivery system during progressive phases of releasing anddelivering a stent according to the disclosed technology.

FIG. 3 is a perspective view of one embodiment the distal end of themoveable sheath according to the disclosed technology.

FIG. 4 is a perspective view of one embodiment the distal end of themoveable sheath according to an alternative embodiment of the disclosedtechnology.

FIG. 5 is a perspective view of one embodiment the distal end of themoveable sheath according to another alternative embodiment of thedisclosed technology.

FIG. 6 is a perspective view of one embodiment the distal end of themoveable sheath according to another alternative embodiment of thedisclosed technology.

FIG. 7 is a perspective view of one embodiment the distal end of themoveable sheath according to another alternative embodiment of thedisclosed technology.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention relates to an apparatus, system and method for insertionand/or delivery of a stent in a bodily passageway. The invention allowsthe clinician or operator to more accurately deliver the stent byminimizing drift or a shift of position of the stent while passingthrough body lumens prior to delivery. The assembly is suited formedical applications (for example, endoscopic therapy) including in thebiliary tract, the gastrointestinal tract, the urinary tract, and therespiratory tract. In particular, one embodiment of the invention isdirected to an assembly, system and method for delivering anintraluminary prosthesis, such as a stent in a biliary duct.Additionally, an assembly in accordance with the disclosed technologycould be used in the vascular system, urogenital tract, neurologicalsystem (e.g., in the brain) and in the cardiovascular system (e.g., inthe heart) and artificially created lumens. Reference herein to bodilypassageways or lumens may be to vessels or passageways in any of theaforementioned tracts and systems or elsewhere in the body. Whilediscussed below primarily in connection with delivering shape memorystents, the apparatus and systems of the disclosed technology can alsobe used to deliver other types of stents and prostheses (e.g.,stent-grafts). Further, it should be understood that stents, as referredto herein, are not limited to tube like structures.

It should be noted that references herein to the term “distal” are to adirection away from an operator of the subject invention, whilereferences to the term “proximal” are to a direction towards theoperator of the subject invention. Accordingly, when the terms “distal”and “proximal” are used herein in the context of an assembly device thatis being deployed within a body, such as a human body, by an operator,the term “distal” refers to a location within the body that is furtherwithin the body than a location that is “proximal” to the operator.

With reference to the drawings, FIG. 1 illustrates an apparatus 100,which is a catheter delivery system used in some embodiments for shapememory tubular stents. Alternatively, the apparatus 100 can be used withnon-shape memory stents that soften with the application of heat orwhose shape is manipulated in other ways. Apparatus 100 includes aflexible catheter 10, a sheath member 20, an expansion member 30 andcontrol elements 40 for activating and deactivating the expansion member30. The middle section of the catheter 10 is removed from theillustration in order to show more detail of the proximal and distalends of the apparatus 100. At the distal end, mounted on the expansionmember 30 is an expandable stent 50 intended for insertion within apatient.

The elongate catheter 10 may be a flexible tube that is inserted into abody lumen or duct and is capable of reaching a target stent deliverylocation. Also, the catheter 10 may include at least one inner passageallowing drainage/injection of fluids and/or access by surgicalinstruments or wiring. The proximal end of the catheter 10 may beprovided with openings 12 communicating with one or more passagesrunning through the catheter 10. In this way, an inner passage can bededicated to fluid flow, while other passages can be dedicated to wiresor other control elements for the expansion member 30 at the distal end.

The sheath member 20 may surrounds and extends along a substantialportion of the catheter 1O. At its proximal end the sheath member 20 mayinclude a handle 28 which may allow an operator to manipulate andcontrol the sliding movement of the sheath 20 relative to the catheter10. The handle 28 and inner catheter 10 may include locking features(not illustrated) for at least temporarily securing those two elementsrelative to one another. Sheath 20 may be designed for entry into thebody, and transluminal travel to a selected site in a body passageway.To this end, the sheath can be pliable in the sense that it readilybends to accommodate curved or serpentine luminal passages, yet hassufficient axial stiffness to allow control of the transluminal travelfrom the proximal end of the sheath. An inner sheath lumen can runlongitudinally through the length of the sheath 20.

Also, sheath 20 can be preferably formed of a body compatible material.Desirably, the biocompatible material is a biocompatible polymer.Examples of suitable biocompatible polymers include, but are not limitedto, polypropylene (PP), polytetrafluoroethylene (PTFE), polyethyleneterephthalate (PET), high density polyethylene (HDPE) and the like.Additionally, the sheath 20 could have layers, coverings, films,coatings, and the like, desirably a polymeric covering, disposed overthe outer or inner surfaces to improve interaction with the body lumenand the inner elements discussed below. Further, the sheath 20 or selectportions thereof could be clear, opaque, translucent, colored and/ornon-transparent as desired.

Additionally, it should be understood that the materials of the sheath20 as well as any component filaments of the sheath 20 can be furtherenhanced with coverings, films, coatings, surface modifications and/orstructures and other materials and techniques. A covering may becomposed of polymeric material and/or silicone. The covering may alsocomprise any plastic or polymeric material, including a somewhat hardbut flexible plastic or polymeric material. The covering may betransparent or translucent, desirably substantially or partiallytransparent. Furthermore, the covering may be constructed of anysuitable biocompatible materials, such as, but not limited to, polymersand polymeric materials, including fillers such as metals, carbonfibers, glass fibers or ceramics. Useful covering materials include, butare not limited, polyethylene, polypropylene, polyvinyl chloride,polytetrafluoroethylene, including expanded polytetrafluoroethylene(ePTFE), fluorinated ethylene propylene, fluorinated ethylene propylene,polyvinyl acetate, polystyrene, poly(ethylene terephthalate),naphthalene dicarboxylate derivatives, such as polyethylene naphthalate,polybutylene naphthalate, polytrimethylene naphthalate andtrimethylenediol naphthalate, polyurethane, polyurea, silicone rubbers,polyamides, polyimides, polycarbonates, polyaldehydes, polyether etherketone, natural rubbers, polyester copolymers, styrene-butadienecopolymers, polyethers, such as fully or partially halogenatedpolyethers, and copolymers and combinations thereof. The coating orcoatings may be on the entire sheath 20 or portions thereof.

The expansion member 30 can be preferably a balloon element that can beinflated and deflated in a controlled manner in order to deploy thestent 50. Examples of balloons used as expansion members 30 aredescribed in U.S. Pat. No. 5,191,883 to Lennox et al. (Lennox) and U.S.Pat. No. 6,830,599 to Schock. The activation of the expansion member 30from a contracted state to an inflated/expanded state and vise-versa maybe regulated by control elements 40. Only a distal portion of theoverall control elements 40 are illustrated in the drawings. Inparticular, the two elements 40 illustrated in FIGS. 1-2 representelectrodes for activating the expansion member 30. At least oneelectrode is needed for this manner of delivery. Such electrodes arepreferably part of a contemporary hot-balloon catheter control system asdescribed in Lennox. However, it should be understood that other ballooncatheter techniques or even other mechanical equivalents can be used asan expansion member with control elements in accordance with thedisclosed technology.

Additionally, the elements 40 also may include radiopaque markers. Theradiopaque markers can either be incorporated with the electrodesdescribed above or disposed in proximity thereto. Preferably, a pair ofelectrodes and a pair of markers are included in the distal end of thecatheter 10. The electrodes can also be radiopaque, thus eliminating theneed for separate markers. The markers 40 can assist the physician oroperator in visualizing the relative position of the delivery portion ofthe apparatus 100 with relation to the target delivery location. Suchmarkers 40 can be formed from radiopaque materials, such asmetallic-based powders or ceramic-based powders, particulates or pasteswhich may be incorporated into the distal catheter material. Forexample, the radiopaque material may be blended with the polymercomposition from which the polymeric filament is formed, andsubsequently fashioned into a portion of the catheter 10. Alternatively,the radiopaque material may be applied only to the surface of thecatheter 10. As a further alternative, the radiopaque material may beattached to the stent (for example, attached or clipped-on mechanicallyor chemically through adhesives, etc.) Various radiopaque materials andtheir salts and derivatives may be used including, without limitation,bismuth, barium and its salts such as barium sulfate, tantalum,tungsten, gold, platinum and titanium, to name a few. Additional usefulradiopaque materials may be found in U.S. Pat. No. 6,626,936, which isherein incorporated by reference. Metallic complexes useful asradiopaque materials are also contemplated. The markers 40 may be theonly portion made radiopaque or the entire distal portion of thecatheter 10 can be made radiopaque. Further, the distal portion of thecatheter 10 may have an inner core of tantalum, gold, platinum, iridiumor combination of thereof and an outer member or layer of nitinol toprovide a composite filament for improved radiocapicity or visibility.Alternatively, portions of the catheter 10 may designed for improvedexternal imaging under magnetic resonance imaging (MRI) and/orultrasonic visualization techniques. MRI is produced by complexinteractions of magnetic and radio frequency fields. Materials forenhancing MRI visibility include, but are not limited to, metalparticles of gadolinium, iron, cobalt, nickel, dysprosium, dysprosiumoxide, platinum, palladium, cobalt based alloys, iron based alloys,stainless steels, or other paramagnetic or ferromagnetic metals,gadolinium salts, gadolinium complexes, gadopentetate dimeglumine,compounds of copper, nickel, manganese, chromium, dysprosium andgadolinium. To enhance the visibility under ultrasonic visualization thearea represented by markers 40 of the disclosed technology may includeultrasound resonant material, such as but not limited to gold.

Also illustrated in FIG. 1 is the stent 50. The stent 50 can be formedof plastics, metals or other materials, it is preferred that abiocompatible construction is employed. Useful synthetic biocompatiblepolymeric materials include, but are not limited to, polyesters,including polyethylene terephthalate (PET) polyesters, polypropylenes,polyethylenes, polyurethanes, polyolefins, polyvinyls,polymethylacetates, polyamides, naphthalane dicarboxylene derivatives,silks and polytetrafluoroethylenes. The polymeric materials may furtherinclude a metallic, a glass, ceramic or carbon constituent or fiber.Useful and nonlimiting examples of bioabsorbable or biodegradablepolymeric materials include poly(L-lactide) (PLLA), poly(D,L-lactide)(PLA), poly(glycolide) (PGA), poly(L-lactide-co-D,L-lactide) (PLLA/PLA),poly(L-lactide-co-glycolide) (PLLA/PGA), poly(D,L-lactide-co-glycolide)(PLA/PGA), poly(glycolide-co-trimethylene carbonate) (PGA/PTMC),polydioxanone (PDS), Polycaprolactone (PCL), polyhydroxybutyrate (PHBT),poly(phosphazene) poly(D,L-lactide-co-caprolactone) PLA/PCL),poly(glycolide-co-caprolactone) (PGA/PCL), poly(phosphate ester) and thelike. Useful biocompatible materials include but are not limited tobiocompatible metals, biocompatible alloys, biocompatible polymericmaterials, including synthetic biocompatible polymeric materials andbioabsorbable or biodegradable polymeric materials, materials made fromor derived from natural sources and combinations thereof. Usefulbiocompatible metals or alloys include, but not limited to, nitinol,stainless steel, cobalt-based alloy such as Elgiloy, platinum, gold,titanium, tantalum, niobium, polymeric materials and combinationsthereof. These alloys may also be doped with small amounts of otherelements for various property modifications as may be desired and as isknown in the art. Further, the stent 50 may include materials made fromor derived from natural sources, such as, but not limited to collagen,elastin, glycosaminoglycan, fibronectin and laminin, keratin, alginate,combinations thereof and the like. Alternatively, a portion of the stent50 may comprise a resilient spring-like metal for self-expansion, whilea second portion is a deformable metal for final sizing. It should beunderstood that shape memory elements may be discrete or merelydifferent phases of an alloy.

Referring to FIG. 2A-2B, apparatus 100 is illustrated in various stagesof deployment of stent 50. FIG. 2A illustrates the distal end of theapparatus 100 with the stent 50 mounted thereon for delivery.Preferably, the configuration illustrated may be maintained while thephysician inserts and tracks the apparatus 100 to the desired locationwithin the patient. The expansion member 30, in the form of anexpandable balloon may be secured at two ends 30 a and 30 b to thecatheter 10. The expansion member 30 is illustrated in adeflated/collapsed state. The expansion member 30 may be positioned tocover and contain the electrodes 40, which are part of the controlassembly for actuating the expansion of the balloon 30. The location ofeach electrode 40 may include radiopaque markers. In this way, the areabetween the two markers 40 represents the delivery portion of thecatheter. Thus, by mounting the stent 50 over the delivery portion, thephysician can use the markers 40 to track and accurately position thestent 50 in the patient.

Also illustrated in FIG. 2A is sheath member 20 disposed radiallyadjacent and axially surrounding the stent 50. Prior to insertion withinthe patient, distal sheath end 20 a may be positioned to abut theproximal stent end 50 a, as shown. Alternatively, a distal portion ofthe sheath 20 can be configured to hold and axially surround the stent50, expansion member 30 and the distal end of the catheter 10. In thisalternative design, the sheath 20 can then be pulled back to theposition illustrated in FIG. 2A, just prior to expansion of the stent50. Once positioned as illustrated in FIG. 2A, preferably either designallows the sheath handle 28 to be secured relative to the catheter 10 inorder to limit axial movement of the stent 50 relative to the deliveryportion.

FIG. 2B illustrates the expansion member 30 expanded, thereby expandingthe stent 50 to a desirable radius R. It should be noted that whileradius R, illustrated in FIG. 2B, is preferably larger than the smallercompressed radius r, illustrated in FIG. 2A, the actual dimensions canvary from those illustrated in the drawings. In other words, thedimensions illustrated are for exemplary purposes only, and the actualdimensions would be designed and configured to conform to the intendedstent application. The control assembly 40 is carefully regulated toensure the requisite expansion dimensions for the stent 50. Duringexpansion, it may be desirable to use a balloon 30 that expands into adog-bone shape, as illustrated, in order to further maintain the stent50 generally centered between the markers 40. Alternatively, a cage,basket or other device could be used to expand the stent 50.

FIG. 2C illustrates the apparatus 100 after the stent 50 has beenexpanded and the expansion member 30 has been partially contracted ordeflated. Also illustrated is an example of when expansion member 30 canget caught or stuck on the stent 50. To assist in separating theexpansion member 30 from the stent 50, the sheath 20 can be advanceddistally into the expanded stent 50. This may help pull the expansionmember 30 away from the stent 50 without moving the stent 50 out ofposition. Once the sheath 20 is advanced distally beyond the stent orwhen the physician is confident the expansion member 30 is not stuck tothe stent 50, the entire delivery system can be pulled back, asillustrated in FIG. 2D, or completely withdrawn. In this way, the stent50 should remain in its intended delivery location and the apparatus 100can be safely removed. Additionally, prior to removal the sheath 20could be used to deliver relatively hot, cold or thermally neutralfluids.

FIGS. 3-7 illustrates various embodiments of the distal end of thesheath member 20. FIG. 3 illustrates a sheath member 20 with acontinuous circular cross-section. FIG. 4 illustrates a sheath member 21whose distal end 21 a bulges radially outward. The bulging end 21 a canfurther assist in separating the stent 50 from the expansion member 30after delivery.

FIG. 5 illustrates a sheath member 22 whose distal end 22 a flaresradially outwardly, like a funnel or cone. A flared distal end 22 a canalternatively be used as an anchor against the proximal end of theexpanded stent 50. Thus, the sheath 22 can prevent further stentmovement as the expansion member 30 is pulled back inside the sheath 22.It should be understood that the pitch and length of the flared distalend 22 a can vary as suited for the particular stent and deliveryconditions.

FIGS. 6 and 7 illustrate further alternative sheath members 23, 24 whosedistal ends include cutouts or slits 23 a, 24 a. The slit 23 a may havea rounded end while the slit 24 a may have a straight taper. However, itshould be understood that slits with other shapes could also beadvantageous. The slits 23 a, 24 a can further assist in separating theexpansion member 30 from the expanded stent 50. Additionally, the slits23 a, 24 a can used to maintain a desired rotational relationshipbetween the stent 50 and the delivery system 100. In other words, inaddition to preventing the stent from sliding axially in the proximaldirection relative to the catheter 10, the slit can prevent the stentfrom rotating relative to the catheter 10 via the expansion member 30.Distal end of sheath may be rounded to assist forward movement.

Further, it should be understood that further techniques can be used inconjunction with the apparatus, system and methods described above, toensure and facilitate accurate stent delivery. For example, alteringballoon materials, applying a lubricant between the balloon and stentand/or leaving out pre-shrinking when mounting the stent on the balloon,can reduce sticking between the stent and the balloon. Similarly,changing how the balloon is folded into its compressed state, such asreducing or reorienting the wing folds of the balloon, can furtherassist in this regard. Sheath may have varying stiffness, varyingreinforced layers, reinforcement, varying wall thickness, varyingdiameters, varying cross-sectional geometry.

While various embodiments of the present invention are specificallyillustrated and/or described herein, it will be appreciated thatmodifications and variations of the present invention may be effected bythose skilled in the art without departing from the spirit and intendedscope of the invention.

1. An apparatus for delivering an expandable stent into a patientthrough a body lumen, the apparatus comprising: a flexible catheter fordelivering the stent, the catheter having a stent delivery portion at adistal end thereof; an expansion member secured to the stent deliveryportion of the catheter, the expansion member adjustable between acollapsed state and an expanded state, the expandable stent mounted onand circumferentially surrounding at least a portion of the expansionmember, whereby adjustment of the expansion member from the collapsedstate to the expanded state causes radial expansion of the stentrelative to a longitudinal axis of the stent; a control assembly foractuating the expansion member between the collapsed and the expandedstates; and a sheath circumferentially surrounding a portion of thecatheter for limiting movement of the stent relative to the catheterduring delivery.
 2. The apparatus of claim 1, wherein the expansionmember is a balloon.
 3. The apparatus of claim 2, wherein the balloonincludes two opposed ends that when inflated during delivery are widerthan a central portion of the balloon.
 4. The apparatus of claim 1,wherein the sheath is moveable along a length of the catheter.
 5. Theapparatus of claim 1, wherein the sheath is securable relative to thecatheter for limiting the stent movement.
 6. The apparatus of claim 1,wherein a distal end of the sheath abuts a proximal end of the stent. 7.The apparatus of claim 1, wherein a distal end of the sheath is radiallywider than a central portion of the sheath.
 8. The apparatus of claim 1,wherein a distal end of the sheath flares radially outwardly.
 9. Theapparatus of claim 1, wherein a distal end of the sheath includes a slitpassing through a wall of the sheath.
 10. An assembly for delivering astent into a patient through a body lumen, the assembly comprising: anexpandable stent; a flexible catheter for delivering the stent; anexpansion member secured to a distal end of the catheter, the expansionmember adjustable between a collapsed state and an expanded state, thestent mounted on at least a portion of the expansion member, wherebyadjustment of the expansion member from the collapsed state to theexpanded state causes radial expansion of the stent relative to alongitudinal axis of the stent; a control assembly for actuating theexpansion member between the collapsed and the expanded states; and asheath circumferentially surrounding a portion of the catheter forlimiting movement of the stent in at least the proximal directionrelative to the catheter.
 11. The apparatus of claim 10, wherein theexpansion member is a heat actuated balloon.
 12. The apparatus of claim11, wherein the balloon includes two opposed ends that when inflatedduring delivery are wider than a central portion of the balloon.
 13. Theapparatus of claim 10, wherein the sheath is moveable along a length ofthe catheter.
 14. The apparatus of claim 10, wherein the sheath issecurable relative to the catheter for limiting the stent movement. 15.The apparatus of claim 10, wherein a distal end of the sheath abuts aproximal end of the stent.
 16. The apparatus of claim 10, wherein adistal end of the sheath is radially wider than a central portion of thesheath.
 17. The apparatus of claim 10, wherein a distal end of thesheath flares radially outwardly.
 18. The apparatus of claim 10, whereina distal end of the sheath includes a slit passing through a wall of thesheath.
 19. A method for delivering an expandable stent into a patientthrough a body lumen comprising: providing a flexible balloon catheterfor delivering the stent, the catheter including an expandable balloon,a control assembly and an outer sheath, the balloon secured to a distalend of the catheter, the balloon adjustable between a collapsed stateand an expanded state, the control assembly for adjusting the expansionmember between states; mounting a stent on the balloon in the collapsedstate, wherein a distal end of the sheath abuts a proximal end of thestent for limiting movement of the stent in at least the proximaldirection relative to the catheter; inserting the flexible catheter andstent into a patient through a body lumen, while maintaining a fixedrelative position between the stent and the catheter; activating thecontrol assembly to expand the stent; and withdrawing the ballooncatheter after the stent has expanded.
 20. The method according to claim19, further comprising the step of advancing the sheath distally insidethe stent prior to withdrawing the catheter.